#include "tss.h"
#include "print.h"
#include "string.h"

// #define PG_SIZE 4096

/* 任务状态段tss结构 */
struct tss {
    uint32_t backlink;
    uint32_t *esp0;
    uint32_t ss0;
    uint32_t *esp1;
    uint32_t ss1;
    uint32_t *esp2;
    uint32_t ss2;
    uint32_t cr3;
    uint32_t (*eip)(void);
    uint32_t eflags;
    uint32_t eax;
    uint32_t ecx;
    uint32_t edx;
    uint32_t ebx;
    uint32_t esp;
    uint32_t ebp;
    uint32_t esi;
    uint32_t edi;
    uint32_t es;
    uint32_t cs;
    uint32_t ss;
    uint32_t ds;
    uint32_t fs;
    uint32_t gs;
    uint32_t ldt;
    uint32_t trace;
    uint32_t io_base;
};
static struct tss tss;

/* 更新tss中esp0字段的值为pthread的0级栈 */
void update_tss_esp(struct task_struct *pthread) {
    tss.esp0 = (uint32_t *)((uint32_t)pthread + PG_SIZE);
}

/* 创建gdt描述符 */
static struct gdt_desc make_gdt_desc(uint32_t *desc_addr, uint32_t limit, uint8_t attr_low, uint8_t attr_high) {
    uint32_t desc_base = (uint32_t)desc_addr;
    struct gdt_desc desc;
    desc.limit_low_word = limit & 0x0000ffff;
    desc.base_low_word = desc_base & 0x0000ffff;
    desc.base_mid_byte = ((desc_base & 0x00ff0000) >> 16);
    desc.attr_low_byte = (uint8_t)(attr_low);
    desc.limit_high_attr_high = ((limit & 0x000f0000) >> 16) + (uint8_t)(attr_high);
    desc.base_high_byte = (desc_base >> 24);
    return desc;
}

/* 在gdt中创建tss并重新加载gdt */
void tss_init(void) {
    put_str("tss_init start\n");
    uint32_t tss_size = sizeof(tss);
    memset(&tss, 0, tss_size);
    tss.ss0 = SELECTOR_K_STACK;
    tss.io_base = tss_size; //无io位图

    *((struct gdt_desc *)0xc0000920) = make_gdt_desc((uint32_t *)&tss, tss_size - 1, TSS_ATTR_LOW, TSS_ATTR_HIGH); //0x900 + 0x08*4 = 0x920, tss

    *((struct gdt_desc *)0xc0000928) = make_gdt_desc((uint32_t *)0, 0xfffff, GDT_CODE_ATTR_LOW_DPL3, GDT_ATTR_HIGH); //0x900 + 0x08*5 = 0x928, user data

    *((struct gdt_desc *)0xc0000930) = make_gdt_desc((uint32_t *)0, 0xfffff, GDT_DATA_ATTR_LOW_DPL3, GDT_ATTR_HIGH); //0x900 + 0x08*6 = 0x930, user code

    uint64_t gdt_operand = ((8 * 7 - 1) | ((uint64_t)((uint32_t)0xc0000900)) << 16);
    asm volatile("lgdt %0"
                 :
                 : "m"(gdt_operand));
    asm volatile("ltr %w0"
                 :
                 : "r"(SELECTOR_TSS));

    put_str("tss_init and ltr done\n");
}